TRIPOLI (Reuters) - Libyan authorities are processing a request from Britain to extradite the brother of the bomber who killed 22 people in Manchester in May, but no decision has been taken yet, a government spokesman said on Thursday.

The armed group holding the brother said that if the attorney general’s office agreed to the request, the force would be “ready for the next step”.

Salman Abedi, a 22-year-old Briton born to Libyan parents, blew himself up at the end of a show by U.S. singer Ariana Grande in the deadliest militant attack in Britain for 12 years. His victims included seven children. More than 500 people were injured.

On Wednesday, British police said they had issued an arrest warrant for his brother, Hashem Abedi, for murder, attempted murder and conspiracy to cause an explosion, and prosecutors had asked Libya to extradite him.

“An official request has been received through the Libyan ministry of foreign affairs and the Libyan authorities are cooperating to process (the request) in accordance with Libyan legal procedures,” said Hassan al-Houni, a spokesman for the internationally recognised government in Tripoli.

“No decision has been taken yet.”

Days after the attack, the Special Deterrence Force (Rada), a counter-terrorism and anti-crime group aligned with the government, arrested Hashem Abedi and the brothers’ father Ramadan. The father was released in August.

Various armed factions in Tripoli have aligned themselves with the government, some with semi-official status for law enforcement. However, the government, which struggles to impose its authority, has limited power over them.

Rada initially said it would not extradite Hashem, but then said it was ready to cooperate.

“If there is agreement between the attorney general and the British authorities, we are ready for the next step,” spokesman Ahmad Ben Salim said.

The Libyan attorney general’s office could not be reached for comment.

Islamic State said it was responsible in the immediate aftermath of the bombing but security services have always treated the claim with scepticism.

In June, Rada said Hashem Abedi had told them his brother had been radicalised in Britain in 2015.

They had both flown from Britain to Libya in April and Hashem said he had helped buy the equipment necessary for the attack although he had not known that Salman was planning a bombing, Rada said.

British police say Salman Abedi returned to Manchester on May 18, four days before his attack.

The family had emigrated to Britain during the rule of the late Libyan leader Muammar Gaddafi. The brothers’ parents returned to Libya during the 2011 revolution.

Police have previously said they believed Salman Abedi had built the bomb himself and CCTV showed him buying nuts from a hardware store that were used as shrapnel as well as the tin that was believed to contain the explosives.